562 
LECTURES ON THE BRITISH PHARMACOPEIA. 
was in both the Edinburgh and Dublin Pharmacopoeias, its exclusion could not 
fairly be insisted on. Should its medicinal use become more general than at pre¬ 
sent, it will probably be retained in a future edition of the British Pharmacopceia; 
in that case, the process given for its preparation will doubtless be improved. It is 
said to be successfully manufactured on the Continent by Melsen’s method, which 
consists in distilling binacetate of potash at a temperature which may vary from 
300° Fahr. to 550° Fahr. (International Exhibition ; Jurors’ Report, Class II., 
Section A., and Chem. News, vol. ix. p. 58). 
Acidum Benzoicum. —The process given for the preparation of benzoic acid, 
namely, heating benzoin in a subliming apparatus, has been frequently proved 
to be a wasteful one, much acid remaining in the non-volatile residue. It is the 
(Edinburgh and Dublin process, but has been much improved since the last 
Pharmacopoeias of those cities were published, and it is to be regretted that the 
British Pharmacopoeia does not exhibit the improvement. If the benzoin be 
boiled with lime and the resulting solution be treated with hydrochloric acid, a 
precipitate is obtained, which yields on sublimation nearly all the benzoic acid 
originally present in the resin. 
Acidum Citricum. —In the method for obtaining Acidum Citricum , the 
British Pharmacopoeia does exhibit the improvements which have been made of 
late years in the manufacture of this acid ; the lemon juice being now ordered 
to be fermented before the citric acid is taken out of it by the addition of the 
carbonate of lime. Personne has, however, observed (Pliarm. Journ. vol. xii. 
p. 548), that citrate of lime itself ferments and yields acetic and butyric, as well 
as carbonic acids, so that it is important to observe, as a note to the Pharma¬ 
copceia process, that fermentation must be quite complete before the carbonate 
of lime is added. 
Acidum IIydbochloricum.— The framers of the British Pharmacopoeia have 
been sharply reproved, for having, in the directions for preparing Acidum Hi/dro- 
chloricum , page 167 of the octavo edition, omitted all mention of the application 
of that heat, without which certainly but little acid will be obtained. In ex¬ 
planation of the omission, I have been told by a high authority that the little 
word “ distil ” was accidentally left out from the end of the fourth line on that 
page. [The error is corrected in the smaller edition recently published.] 
Acidum IIydrocyanicum Dilutum. —Many processes have been recom¬ 
mended for the preparation of this acid, but that of the three old Pharmacopoeias 
has, I think, been wisely retained. The product is not absolutely pure, as it con¬ 
tains a trace of sulphuric acid, but it has the advantage of being far more stable 
than a pure acid would be,—a fact long well known but only recently explained. 
Millon (Comptes Rendus, vol. liii. p. 842) has shown that the alteration which 
the pure acid is so apt to undergo is caused by the formation of ammonia : that 
a bubble or two of ammoniacal gas would in two or three days completely change 
many thousand times its weight of hydrocyanic acid ; and that the presence of 
other acids or aciclifiable matter preserves hydrocyanic acid either by neutra¬ 
lizing ammonia as soon as it is formed or by preventing its formation. The di¬ 
lute hydrocyanic acid of the London Pharmacopoeia contained two per cent, of 
real acid, that of the Dublin book was rather stronger, while the Edinburgh 
form contained nearly four per cent. The strength of the national acid has been 
fixed at the old London percentage, and we thus now have this most important 
medicinal agent of uniform strength in the three kingdoms. 
Acidum Nitricum.— In the strength of Acidum JSitricum the English pre¬ 
paration has had to give place to that of Scotland and Ireland. It is to be re¬ 
gretted that the Dublin Section of the Pharmacopceia Committee did not profit 
by Redwood’s critical remarks (Pharm. Journ. vol. x. p. 391) on the last Irish 
Pharmacopoeia. He said, “a weaker acid would keep better, and would answer 
every purpose required in pharmacy.” Possibly they thought they had made 
